Temperature measuring apparatus



4, 1952 H. WANNAMAKER, JR 2,616,296

TEMPERATURE MEASURING APPARATUS Filed Oct. 1, 1949 AAA R J mm 3 N N M I A W an L 8 4 m 7 2 2 W 8 5 m 8 E l I Y 2 2 L WT B rmm I W WW H7 6 MTG O 7 MW .l l A 1} 3 0 l 95 l 2 4 2 9 2 3 v m4 W V 3 O 5 4 3 3 D m H 8 W m 2 M .t 3 A ATTORNEY.

Patented Nov. 4, 1952 TEMBERATURE MEASURING. APPARATUS,

William H-.- Wannamaker, J12, Flourtown, Panassigner to. Minneapolis-Honeywell Regulator Gompany,.Minneapolis, Minn.,a corporation of Delaware Application October 1*, 1949; Serial No. 119;060

'l= Claims (01. 73--341) The present invention v trical temperature measuring apparatus, and is specifically concerned withapparatus for the measurement of absolutetemperature ratios bymeans of thermocouples.

The general object of the present invention is to provide an improved apparatus forelectrically mea-suringabsolute temperature ratios. A specific object of the invention is to provide-an improved apparatus for utilizing thermo elec tricelements' or thermocouples in the measurement of the ratio of two-temperatures.

A more specific object of the present invention is to provide apparatus formeasuring the ratio of two temperatures by meansof thermocouples, wherein an additional temperature sensitive eIe-- ment is employed for the purpose of modifying a voltage which varies in accordance with the-dif-- ferencebetween the two temperatures to obtain a measurement ofthe ratio of the two temperatures.

Absolute temperature ratio measuring apparatus of the type disclosed'and claimed herein has utility in many diversified applications; For

exampla in the operation-of largeaxial flow aircompressors, it has been found essentialto have a continuous indication of the absolute temperature ratio of theair inlet and outlet tempera-- tures if the compressor" is--tobe efii-cientlyoperated in a safe manner; That is; it hasbeen-iound;

that when operating a large axial flow compressor under a varying load, the operation of thecompress/or; mayautomatically shift to anunstableportion of itsoperatingcurve. Sucha s'hift'to an unstable operating conditioncreatesa dangerous; situation, since operation beyond the stall point is then likely to occur, causing serious damage or even destruction of the compressor due tothe severe vibration of thecompressor blades produced-by such operation beyond the-stall'point;

Further, it has also been found that the absolute temperature ratio of the I inlet and outlet airtemperaturesof such a compressor is a measure of the efii-c'iency of the compressor operation, and; that, for a given pressure ratio, an;increas ing absolute temperature ratio indicates; a decreasing, effi'ciencyof' operation-and anapproa-ch tea-stall, point and its accompanying hazardous operation. By having available-- a-constant measure of, the absolute temperature ratio, howeyer; a tendency to; unstable operation of the compressor can be quickly noted; andremedial operatihg measures can then betakentoprevent damageto 'theape paratus.

- The: absolutetemperature ratio measurin apbroadly relatestoeleeparatus or the presentinvention is especially well suited for providing a continuousindication of the operating temperature ratioof a compressor for the purpose just described. For'example, the

,. high temperature of the outlet air of such a compressor dictates that a thermoelectric typeof temperature sensitive element be employed for measuringthis temperature: Accordingly the apparatus; of the present invention; which employs thermoelectric elements for the temperature measurements, is extremely well adapted for ficiencies. of, internal. combustion. engines and.

heat exchange pparatus.

Broadly, the novel] temperatur ratio measuring apparatus of the. present invention performs itsrfunction by subjecting, a. first thermoelectric junction. to one; ofqthe two temperatures, whose ratio is-to be measured. to derive afirst. voltage variable; with that one temperature, subjecting a second thermoelectricjunction to the other of saidtemperatures to derive. a second voltage variable with said othertemperature, deriving a.

volt ageiwhich is the differenceof said first and. second voltages, establishing a. variable reference voltage, varying saidreference voltage. in direct proportion. to oneof, said temperatures, and com.- paring saiddifierencevoltage and saidvariedIreference voltage. to obtaina measure of. the ratio of thesaid two temperatures.

Inthe novel, arrangement disclosed in the present application as a preferred form of. apparatus of thepresent invention, a self-balancing. null, type of. voltage l I;esponsive ;measuringdevice is employedfor providing the desired ratio meas.

urement. In the disclosed-1 apparatus, the differenceavoltage: obtainedirom. the: two series-- connected thermoelectric; iunctionsis automatically balanced against an. opposing, reference.

voltage obtained across aip-ortion of. a slide'wire. resistor; Inadditiomthe total referencezvoltage across thisslide-wire resistor is caused-to vary in direct proportion to one of the temperatures under consideration This variati-on in the reference voltage is preferably produced by meansof a resistance thermomete typeor temperature" 3 sensitive element which is connected in the circuit supplying the reference voltage to the slide wire resistor.

Associated with the slide wire resistor is an adjustable contact which is automatically positioned by a reversible electric motor included in the voltage responsive device. The latter is continuously operative to cause this contact to be positioned at any given time at a point on the slide wire resistor at which the portion of the reference voltage between the contact and an end of the resistor is equal and opposite to the thermoelectric difference voltage at that time. Since the reference voltage is also directly proportional to one of the temperatures in question, the position of the contact along the slide Wire resistor is made to be a measure of the ratio of the two temperatures.

In addition to the above, inasmuch as only the two temperatures whose ratio is to be measured are involved in producing the thermoelectric difference voltage, the ratio which is measured by the disclosed apparatus is that of the absolute values of the two temperatures.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use,

reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings the single figure is a modified schematic electrical circuit diagram of a preferred form of the temperature ratio measuring apparatus of the present invention.

The preferred embodiment of the present invention illustrated in the drawing comprises a first thermoelectric junction I, adapted to be subjected to a first temperature, and a second thermoelectric junction 2, adapted to be subjected to a second temperature. The measuring apparatus including the thermoelectric junctions I and 2 is designed to measure the ratio of the absolute values of the two temperatures just'specified.

The thermoelectric junction I is shown as being a portion of a thermocouple 3 and is the junction formed between two thermocouple wires 4 and 5, of dissimilar metals. Similarly, the thermoelectric junction 2 is shown as a portion of a thermocouple 6 having elements I and 8 of dissimilar metals which are joined to form the junction 2. Although various metals may be utilized for the thermocouple wires 4, 5, 1, and 8, these metals must be so chosen that the difference voltage obtained when the thermocouples 3 and 6 are connected in series opposition is a measure of the difference between the two temperatures to which the junctions I and 2 are respectively exposed.

By way of example, it may be noted that in a successfully operating model of the apparatus being discussed, the thermocouples 3 and 6 were iron-Constantan couples. For purposes of illustration, the following description of the disclosed apparatus will refer to the thermocouples 3 and 6 as being of the iron-Constantan type. It should be understood, however, that other thermocouple materials or other types of thermocouples may be employed if desired.

In the apparatus under discussion, the wires and I of the thermocouples are the Constantan wires thereof. The end of the wire 5 remote from the junction I is connected at a junction 9 to one end of a Constantan lead wire I6, the remaining end of which is connected at a junction I I to the end of the Constantan thermocouple wire 1 remote from the junction 2. Since each of the wires 5, I, and I0 is of Constantan, the junctions 9 and II are not thermoelectric junctions but merely serve as electrical connections for the associated wires.

The iron wire 4 of the thermocouple 3 is connected at a junction I2 to one end of a copper conductor I3. Similarly, the iron wire 8 of the thermocouple 6 is connected at a junction I4 to one end of a copper conductor I5. Since the thermoelectric difference between iron and copper can be considered to be negligible, it is apparent that the junctions I2 and I4 serve no thermoelectric purpose, but merely connect electrically the associated wires.

From the foregoing description of the connections to the thermocouples 3 and 6, it should be apparent that the electrical outputs of the junctions I and 2 are connected in series opposition, and hence that the net voltage produced between the conductors I3 and I5 by the junctions I and 2 will be a difference voltage which will vary directly in accordance with the difference between the temperatures to which the junctions I and 2 are subjected.

The difference voltage produced between the conductors I3 and I5 is compared with an adjustable reference voltage for the purpose of determining the ratio between the absolute temperatures in the vicinities of the junctions I and 2. To this end, there is provided a voltage responsive device I6 having an amplifying and motor controlling portion I! provided with a pair of input terminals I8 and I9. The thermoelectric junctions I and 2 and the adjustable reference voltage are connected in series between the input terminals I8 and I9 in the input portion of the voltage responsive device I6 in a manner shortly to be described.

By way of illustration, the voltage responsive device I6 of the disclosed apparatus has been diagrammatically shown as being of the electronic conversion and motor drive type as disclosed in the Wills Patent 2,423,540. For purposes of simplification, the electronic conversion amplifier and motor drive circuit of said Wills patent has been shown in block form as the portion I! of the subject apparatus. Since this electronic conversion and motor drive apparatus and its operation are explained in detail in said Wills patent, it appears necessary only to state herein that a D. C. voltage applied between the input terminals I8 and I9 will be converted by the apparatus into a corresponding alternating current voltage which in turn is amplified and utilized by the apparatus in producing a motor controlling voltage which will appear between a pair of output terminals 20 and 2I of the portion I1.

Associated with the control portion I1 of the voltage responsive device I6 is a reversible electric motor 22 having a. power winding 23, a control winding '24, and a rotor 25. The winding 23 is connected in series with a condenser 26 between alternating current supply conductors 21 and 28 which are operative to supply to the winding 23 a substantially constant voltage of conventional magnitude and frequency. The apparatus portion I1 is also supplied with energizing voltage from the conductors 21 and 28 as shown. The motor control winding 24, however, is connected between the output terminals 20 and 2I or the apparatus portion H and is therefore energized by the motor controlling'voltage produced between these terminals. Inview or the complete disclosure presented in the aforementioned: Wills patent, it isnecessary herein only to state that the motor control voltage produced bythe apparatus portion l 'l causesthe motor control winding- 24 to cooperate with the power windingfl soas to cause rotation of the rotor 25 in a direction corresponding to the polarity ofthe voltage applied between the apparatus input terminals l3 and 19-, and at a speed which. is determined by the magnitude of that voltage;

For the purpose of establishing the aforemem tioned variable reference voltage in the subject.

apparatus; there is provided a slide wire resistor 29 associated with which is an adjustable sliding contact 30. The slide wire resistor 28 is supplied with avariable energizingvoltagefrom a suitable battery; 30' by means of a Wheatstone bridge cii cuit generally designated at 3 I The bridge circuit 3t includes input terminals 32 and 33, output terminals 34- and 35, nontemperatu-re sensitive; resistors 36, 31-, andj 38, and a temperature sensitive; resistor- 39. These elements of the bridge circuit" 31 are connected in the followingmanner; The resistor 38 is connected between the, input terminal 32- and the output terminal 34; while the resistor is con nected' between the output terminar 34 and the input terminal 331 The resistor 38 is connected between the input. terminal; 32 and the output terminal; 35, while the; temperature, sensitive resistor 39 is connected between the output terminal; 35; and theinput, terminal 33*; The, battery 30 is connected in series With an adjustable re-' sistor 40 between the bridge circuit input termihals 32" and 33;;

The bridge circuit outputterminals 34. and 35; are utilized as, the energizing terminals for the slide wire resistor 29. To this end; the.resistor 29; is connected in serieswith,anadj istable re sistor. 4|, betweenthe terminals 341 and135.

Ifhe aforementioned variable reference voltage ith, hich. the t erm couple difierence. voltage s-co paredinthe nputlportiono dev e. I s. obtainedf om hoslioe. wire resistor ibe e 'n ho diustable contact 30' thereof. and the. terminal .35; Accordingly, thecontactfll a'nclgterin l 5. on ti pair of. output, terminals for. the slide wire resistor 29 between, whichmtherel r duc d. iable, reference volta e oil a ma nit o n y epen entupon thomagnitud'e of the energizing voltage applied; tothe slide-wire a etWeenthe. term na s 4 ans-1.135%: the, o tput of, the bridge circuit 3|,ja ndi upon the position of thecontacttlrelative to the end of: the re-' sistor 29' adjacent the termina1135:

The variable reference voltage, appearingbetween thecontactBUfandthe terminal 35 as just describedis arranged to oppose the thermocouple difference voltage in, the input' .p ortion of-the voltage responsive device, [.63 To; this; endgthe aforementionedconductor, l 3,,is connectedflto the slide wire resistorc'ontact 30, while the conductor 15, is connected to the inputterminal IQjof'the.

device Iii. The remaining inputteiimihal, l8of the latter-is connected by aconductor 4230. the

remaining reference voltageterminalj 35,,

mu der hatth variab ere renccvoltago. will oppose th thermocoup ifieronco voltage in the inputof, the device the battery an: is,so connected. to, the, bridge circuit .31 that the bridge circuit input terminal32"is rendered'positive with respect to the terminal 33. The relative re- 6. sistancevalues of the bridge circuit resistors 36;. 31:, 38, and 39' are then so. chosen in a known manner that the bridge circuit output voltage between theterminals 34 and 35 causes the terminal 35 to be positivewith respect to the terminal 34. As a result of this, therefe'rence voltage appearing between the contact: 30 and the: terminal 35 will always be such as to render the contact 30 negative with respect to the terminal 35. Finally, the thermoelectric junction 1 is arranged to be subjected to the lower of the two temperatures whose ratio is to be measured; whereby any difference betweenthosetemperatureswill render the conductor I5 positive-with:

1 respect' to the conductor l '3 byan amount which is directly variablei'n accordance with the temperatu're diiference.

Ifthe circuit connected between the input termin-alsl8 and 19 external to the device 'I'G is traced; it will be seen that the voltages thereinare of the proper relative polarity toproduce-the required'volt'ag'e opposition. Specifically, said external' circuit can be traced from the input tor-- minal' l'iiand through the conductor 4'2" to the positive reference voltage terminal35'; Fromthis terminal the circuit passes through a portion of the slidew'ireresistor-25 tothe contact 3 0; which is negative with respect to theterminal: 35}. Com nected to the terminal 30' is the negative thermocouple conductor l3, and betweenthe conductor l3 and the positiveconductor 15 are connected' in series voltage opposition the thermoelectric-junctions land 2. Finally, the conductor i5 is connected tothe remainingihputtermina l' ['9.

It can readily be seen from the drawing'that whenthe junction 1 is subjecteditothe-lower-of the two temperatures under r'rreasure'm'ent, the conductor l3 will always be negative with re spect to the conductor i5; since under this-condition, the junction 2', which'has-it's-positive wire 8'co'nnectedto the conductor I5 and-has its hega tive wire- 1' connected, to the conductor l3;,wi11 produce a greater voltage between the connec tions H and I4 than will be produced bythe junction l' between theconnections- 9' and I2.

I'he voltage responsive: device It including the motor 22 isoperative-to maintain the reference voltage between the contact 33 and the terminal 35 equalandopposite'at all times-to; thethermocouple difference voltage appearing between'the conductors I3fand l5, To thisehd a mechanical linkage 43 is connected bet'weenthe motor rotor 25 and the contact3fl so that asfithe' rotor 25 rotates, thecont'act 30 iscorrespondingly'adjusted along the length of the slide wire resistor 29]; Accordingly when the contact 30 is ata' position along the slide wire resistor 29 such that the reference voltage is equal in magnitude to the thermocouple difference voltage, no voltage is applied between the input terminals I3 and I9; and the correspondingmotorcontrol signal then roduced by the portion l T iseffectiveto prevent motion ofthe rotor 25' or contact 311': In this condition; the apparatus is saidto be in balance;

Upon'a change in the'magnitudeofthethermo cou le difference voltage; however; this voltage will'no longer-be equally opposed by the reference voltage; and a net voltage will then appear between the input terminals I8 and [9; This last mentioned voltage will have a magnitude dependent-- upon the difference" between the: ref-- erence voltage and r the thermocouple difference voltage; and will have a polarity dependent upon which of" the two last: mentioned voltages is the" greater. Under this Y condition, the apparatus portion I I will be operative to produce an appropriate motor control voltage-which, in turn, will cause rotation of the rotor 25 in the direction and to the extent necessary to move the slide wire resistor contact 30 to a new position along the resistor 29 at which the balanced condition of the apparatus will be restored, and no voltage will be applied between the input terminals I8 and I9.

In the foregoing description, no account has been taken of the fact that the bridge circuit resistor 39 is temperature sensitive. If it is assumed for the moment that resistor 39 is not temperature sensitive, it can readily be seen that for a constant energizing voltage applied between the bridge circuit input terminals 32 and 33, the voltage between the slide wire resistor energizing terminals 34 and 35 will be constant at all times. If this were the case, the voltage responsive device I would be operative to position the adjustable contact 39 along the slide wire resistor 29 solely in accordance with the diiference voltage of the thermoelectric junctions I and 2. Under this condition, the position of the contact 30 relative to the lower, positive end of the resistor 29 would then be a measure of the difference, but not the ratio, of the two temperatures to which the junctions I and 2 are respectively subjected.

In the ratio measuring apparatus of the present invention, however, the energizing voltage for the slide wire resistor 29 produced between the terminals 34 and 35 is not maintained at a constant value at all times. made to vary in direct proportion to one of the two temperatures under consideration. In order to accomplish this, the bridge circuit resistor 39 is made a temperature sensitive resistor as noted hereinbefore, and is positioned closely adjacent to the thermoelectric junction I so as to be subjected to substantially the same temperature as the junction I. From a consideration of the illustrated bridge circuit 3|, it is obvious that for a constant energizing voltage applied between the terminals 32 and 33, the bridge circuit output voltage, which is the energizing voltage for the slide wire resistor 29, will vary in direct proportion to the resistance value of the resistor 39. Since the resistor 39 is chosen so as to exhibit a suitable relationship between its resistance and the temperature to which it is subjected, the voltage between the terminals 34 and 35, and hence the reference voltage between the contact 30 and the terminal 3-5, are caused to vary in direct proportion to the temperature to which the junction I is subjected.

The effect of so varying the reference voltage in accordance with one of the two temperatures being measured is to cause the contact 39 to be positioned along the resistor 29 in accordance with the ratio of the two measured temperatures, rather than in accordance with the difference between these temperatures. To illustrate this, let it be assumed that the two temperatures under consideration are equal at some given time. Under this condition, the difference voltage between the conductors I3 and I will be equal to zero, and the device IE will position the contact 39 at the extreme positive end of the resistor 29, since this is the only point along the last mentioned resistor at which zero reference voltage can be obtained. That this will occur can readily be seen when it is noted that for a difference voltage of zero, a reference voltage of zero value is Instead, this voltage is the only one which will produce a zero input voltage to the device I6 and produce a balanced condition of the apparatus.

It is obvious that a difference voltage of zero indicates equality between the two temperatures to which the junctions I and 2 are respectively subjected. Therefore, a zero difference voltage represents a temperature ratio of 1. Consequently, the position of the contact 30 at the extreme positive end of the slide wire resistor 29 can be calibrated as the point representing the measured absolute temperature ratio of 1. That the contact 39 will assume this position for any condition of equality between the two measured temperatures, no matter what the absolute value of the temperature, is readily seen from the fact that no matter what the resistance of resistor 39, and hence no matter what the magnitude of the voltage between the terminals 34 and 35, the point at the extreme positive end of the resistor 29 will be the only point at which the reference voltage determined by the position of the contact 39 will be zero.

As a further illustration of the operation of the present invention, let it be assumed that the thermoelectric junction I and temperature sensitive resistor 39 are subjected to a temperature of 800 F. Let it also be assumed that the temperature to which the junction 2 is subjected is 1600 F. Under this condition, the temperature difference as exemplified by the difference voltage between the conductors I3 and I5 will be 800 F. and the contact 30 will be positioned at a point which can be calibrated to indicate the existing absolute temperature ratio of 2. The voltage between the terminals 34 and 35 and hence the reference voltage between the contact 39 and terminal 35 will have fixed values corresponding to the temperature of 800" F. to which the resistor 39 is subjected.

If it is now assumed that the temperature to which the junction I and resistor 39 are subjected increases from 800 F. to 1200 F., and at the same time the temperature to which the junction 2 is subjected increases from 1600 F. to 2000 F., the difference voltage between the conductors I3 and I5 will remain the same, since the measured temperature difference is still 800 F. Were it not for the operation of the resistor 39, the contact 39 would remain in the last mentioned position representing a temperature difference of 800 F. and a temperature ratio of 2, since the reference voltage would not have changed with the temperature, and since the difference voltage would remain the same. However, the ratio indication provided by the apparatus would then be in serious error, since the new ratio of the temperatures is no longer 2, but has been reduced to 1.67.

The resistor 39 of the present invention is operative, however, to prevent such errors in the ratio measurements made by the apparatus. In the above illustrative example, when the temperature at the junction I and resistor 39 changes from 800 F. to 1200 F., the resistance of the resistor 39 will increase correspondingly, and hence the voltage between the terminals 34 and 33 will be increased an amount directly proportional to the temperature increase at the resistor 39. This, in turn, will cause an increase in the reference voltage between the contact 30 and the terminal 35, even though the contact 30 remains momentarily at the point indicating a temperature ratio of 2 and a temperature difference of 800,F.

existing temperature ratio the battery 30'.

when this occu'rs it can 'easilybe seen that the apparatus win no longe be in bala'nce, since the reference voltage will have increased while [the difference voltage will have remained un- "changed. Accordingly, aninput voltage will be roduced between the terminals l8 and I9 havmg a polarity such that the motor 22 win aajust the contact 30 to a new'position closer to the'po'sitive end of the resistor 29, at which position the reference Voltage will again just oppose the difference voltage and the apparatus will once more be in balance. In moving to its new position, the contact 30 will have left the point indicating a ratio of 2 and will have moved toward the point indicating a "ratio of 1. The new point at which the device IE will position the contact 30 can then be calibrated to indicate the v or 1.67.

I From the above descri tion it should'beevident that the apparatus ofthe present invention' is operative to provide an indication of the ratio ofrtwo measured temperatures'by first ascertaining a difierence voltagev'vhich is a function ,of the difference orthe two temperatures, and then by comparing this difference voltage with a reference voltage which has been varied in accordance with one of the two measured temperatures.

bridge circuit energizing voltage in order to maintain the latter constant. If desired, the resistor to may be automatically adjusted to maintain constant the bridge circuit energizing voltage as is done and explained in thaforementioned Wills patent.

The adjustable resistor 4| is providedin the present invention in series with the slide wire resistor 29 for the purpose of, permitting initial calibration of the apparatus. After the apparatus is calibrated, no further adjustments need the givento the resistor 44' unless the length of the conductors connected to the resistor 39 is changed substantially.

It is believed to be a arent that the two thermocouples a and 6 of the disclosed embodimentof the present invention could, desired, bereplace'dby a single thermocouple formed of suitable materials. For example, asing l ecopperficnstantan thermocouple could be connectedbetween the conductors l3 and 15 at the junctions i2 and M in lieu f the thermocouples 3 and If this were done, with the copper wire of the new thermocouple connected to the copper condoctor I-3 at the junction, l2, this junction would not. be thermoelectric. The copper-Constantan junction of the thermocouple would then be a thermoelectric junction which would be subjected to the first temperature to be measured in lien or the junction i. Finally, the Constantan wire of the thermocouple would be connected to the: junction M, and. this" junctionwould form 'a second thermoelectric t junction which would replace the" junction 2 subjected to the second of the twomeasured temperatures,

By way or example and illustration, and" not by way of limitation, the folio is a listof the component values for the various elementsof the '10 aforementioned operating model constructed in accordance with the present invention:

Resistor 29, 200 ohmslide wire Resistor 36, 32.6, ohms Resistor 31, 565 ohms Resistor38, 14.2 ohms Resistor 39, Brown Instrument Co. type A nickel resistance thermometer bulb; 507.5 ohms Resistor 40, 200 ohm adjustable Resistor 4|, ohm adjustable Battery 30, 1.5 volts (average) Thermocouple wires 4 and 8, iron Thermocouple wires 5, I; and I0; Consta'ntan 'While, in accordance with the provisions of the statutes, I have illustrated and described the best form of the invention now known to me, it

will be apparent to tho e skilled in the art that changes may be made'in the form of the apparams disclosed without departing from the spirit of the inventionas'set forth in the appended cla ms, and that in'some cases certain features of the invention maysometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is: g

1. Anabsolute temperature ratio measuring device comprising a firsttherrno'electric junction adapted to be 'subjected to a first temperature, a secon i thermee1ectric junction adapted to be subjected toga second temperature, adjustable referencevoltage means having energizing terinit als adapted to be connected to a source of energizing voltage and, having a pair of output terminals between which said reference voltage means is operative, when energized from the source, toprovide a voltage of a magnitude jointlydepengient upontlie" magnitude of the voltage applied between said energizing terminals and the adjustment of said means, a temperature sensitive element connected in the energizing connection to sfaid energizing terminals of said reference voltage means, adapted to be subjected tonne of said first and second temperatures, and

' operative to increase the voltage applied between said ene gizing terminals upon an increase in s'ai d one of said' temperatures, a voltage responsive device having a pair of input terminals, and conductor: means" connecting said first and second thermoelectric junctions in series voltage opposition and series with said output terurinals between said input terminals, said voltage responsive, device including adjusting means connected to said adjustable reference voltage and operative to adjust the latter in accordance withv the magnitude and polarity of the resultantvoltage applied between said input terurinals, whereby said adjusting means adjusts said adjustable reference voltage means in aceordance with the; ratio of said first and second temperatures. k

2. f'p aratu's' as specified in claim 1, wherein said adjustable reference voltage means is a slide wire resistor having its end terminals connected between said energizing terminals and having an adjustable contact electrically connected to one of said output terminals, the'othe'r or said output terminals'b'eing connected to one of said energizing t rminals, and wherein said contact is mechanically'linked to said adjusting means of said voltageresponsive device, whereby the latter is operative to adjust said contact along said adapted to be subjected to a first temperature, a

second thermoelectric junction adapted to be subjected to a second temperature, a Wheatstone bridge circuit having a pair of input terminals, a pair of output terminals, and four bridge arms including resistance elements connected between said terminals, one of said elements being temperature sensitive and adapted to be subjected to one of said first and second temperatures, conductors adapted to connect said input terminals to a source of energizing voltage, said bridge circuit being operative, when so energized, to provide between said output terminals a voltage of a magnitude dependent upon the resistance of said one element and which increases when said one of said temperatures increases, adjustable reference voltage means having a pair of energizing terminals and a pair of output terminals, conductors connecting each of said energizing terminals to a respective one of said bridge circuit output terminals, said reference voltage means being operative, when so connected, to provide between the output terminals thereof a voltage of a magnitude jointly dependent upon the resistance of said one element and the adjustment of said means, a voltage responsive device having a pair of measuring terminals, and conductors connecting said first and second thermoelectric junctions in series voltage opposition and in series with the output terminals of said reference voltage means between said measuring terminals, said voltage responsive device including adjusting means connected to said adjustable reference voltage means and operative to adjust the latter in accordance with the magnitude and polarity of the resultant voltage applied between said measuring terminals, whereby said adjusting means adjusts said adjustable reference voltage means in accordance with the ratio of said first and second temperatures.

4. Apparatus as specified in claim 3, wherein said adjustable reference voltage means is a slide wire resistor having its end terminals connected between said bridge circuit output terminals and having an adjustable contact electrically connected to one of the output terminals of said reference voltage means, the other of the last mentioned terminals being connected to one of said bridge circuit output terminals, and wherein said contact is mechanically linked to said adjusting means of said voltage responsive device, whereby the latter is operative to adjust said contact along said slide wire resistor in accordance with the ratio of said first and second temperatures.

5. Apparatus as specified in claim 1, wherein said first thermoelectric junction is the hot junction of a first thermocouple, wherein said second thermoelectric junction is the hot junction of a second thermocouple composed of the same materials as said first thermocouple, each of said thermocouples consisting of a positive wire and a negative wire jointed to form the corresponding hot junction, and wherein one of the wires of said first thermocouple is connected to one of said output terminals, the other of the wires of said first thermocouple is connected to the wire of identical polarity of said second thermocouple, the other wire of said second thermocouple is connected to one of said input terminals, and the other of said output terminals is connected to the other of said input terminals, said hot junctions being the only significantly thermoelectric junctions in the apparatus.

6. Apparatus as specified in claim 1, wherein said voltage responsive device comprises an electronic conversion amplifier having an output portion and an input portion connected between said input terminals, a reversible electric motor having a rotor and energizing terminals, a motor drive circuit having output terminals connected to said motor energizing terminals, having input terminals connected to the output portion of said amplifier, and operative to control the speed and direction of rotation of said rotor in respective accordance with the magnitude and polarity of the resultant voltage applied between the first mentioned input terminals, and a mechanical linkage connected between said motor rotor and said adjustable reference voltage means and operative to adjust the latter in accordance with the magnitude and polarity of said resultant voltage.

'7. An absolute temperature ratio measuring device comprising a first thermocouple having a positive wire and a negative wire joined to form a first hot thermoelectric junction adapted to be subjected to a first temperature, a second thermocouple composed of the same materials as said first thermocouple and having a positive wire and a negative wire joined to form a second hot thermoelectric junction adapted to be subjected to a second temperature, a Wheatstone bridge circuit having a pair of input terminals, a pair of output terminals, and four bridge arms including resistance elements connected between said terminals, one of said elements exhibiting a positive temperature coefiicient of resistance and adapted to be subjected to one of said first and second temperatures, conductors adapted to connect said input terminals to a source of energizing voltage, said bridge circuit being operative, when so energized, to provide between said output terminals a voltage of a magnitude directly dependent upon said one of said temperatures, a slide wire resistor having its end terminals connected between said output terminals and having an adjustable contact, said slide wire resistor being operative, when so connected, to provide between said contact and one of said end terminals a reference voltage of a magnitude jointly dependent upon said one of said temperatures and the position of said contact along said slide wire resistor, an electronic conversion amplifier having an output portion and an input portion including a pair of measuring terminals, a connection between one of the wires of said first thermocouple and said contact, a connection between the other of said wires of said first thermocouple and the wire of identical polarity of said second thermocouple, a connection between the other wire of said second thermocouple and one of said measuring terminals, a connection between said one of said end terminals of said slide Wire resistor and the other of said measuring terminals, said hot junctions being the only significantly thermoelectric junctions in said apparatus, whereby the aforementioned connections are operative to apply between said measuring terminals a resultant voltage dependent in magnitude upon the difference between the reference voltage between said contact and said one end terminal and a difference voltage varying in accordance with the difference between said first and second temperatures, and dependent in polarity upon the relative magnitudes of said difgizing terminals, a motor drive circuit having output terminals connected to said motor energizing terminals, having input terminals connected to the output portion of said amplifier, and operative to control the speed and direction of rotation of said rotor in respective accordance with the magnitude and polarity of the resultant voltage applied between said measuring terminals, and a mechanical linkage connected between said motor rotor and said contact and operative to cause said motor to adjust said contact to positions along said slide wire resistor corresponding trithe, ratio of said first and second temperatures. WILLIAM H. WANNAMAKER, JR.

REFERENCES oIrrEp fi-j rhe following references are" of record in the this patent:

UNITED STATES PATENTS Numloer Name Date 1,617,416 Pierce Feb. 15, 1927 Cherry Mar. 21, 1950 

